? on biasing JFETs

Are JFETs biased differently from standard bipolar transistors? Them must be, or the schematic I have is crap. The gate/drain junction is not biased with reverse polarity, like I am used to with, say, 2N3904s. It looks like it is forward based just like the source/gate junction. Any words of wisdom are welcome. Obvious newbie here...

Thanks,

Dave

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Dave
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Don't assume that the two are mutually exclusive. It could be that JFETs are biased differently from bipolars (they are) *and* the schematic you have is crap.

I hope this helps. :)

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Guy Macon
Reply to
Guy Macon

If the gate is a higher voltage than the drain (assuming the schematic isn't crap) check to see if the JFET is P-channel (analogous to a PNP bipolar).

Generally a JFET will conduct serious current when the gate-source voltage is zero, so you will often see N-channel JFETs biased with a DC path to the negative rail and the source connected to the same rail through a small resistor.

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Tim Wescott
Wescott Design Services
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Tim Wescott

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